Issue #3221516 by quietone, himanshu_jhaloya, smustgrave, Lendude, joachim:...

Issue #3221516 by quietone, himanshu_jhaloya, smustgrave, Lendude, joachim: Improve documentation for $old_destination_id_values in MigrateDestinationInterface

(cherry picked from commit 32e9b0f7)

core/modules/migrate/src/Plugin/MigrateDestinationInterface.php

@@ -98,7 +98,9 @@ public function fields();
    * @param \Drupal\migrate\Row $row
    *   The row object.
    * @param array $old_destination_id_values
-   *   (optional) The old destination IDs. Defaults to an empty array.
+   *   (optional) The destination IDs from the previous import of this source
+   *   row. This is empty the first time a source row is migrated. Defaults to
+   *   an empty array.
    *
    * @return array|bool
    *   An indexed array of destination IDs in the same order as defined in the